1. Field of the Invention
The present invention relates to novel liquid crystal polymers having a high degree of rigidity, and to a process for preparing such polymers.
2. Description of the Prior Art
Liquid crystal polymers are well-known in the art. These polymer exhibit anisotropy in the liquid phase. They may be characterized as thermotropic (i.e., liquid crystal in the melt), or lyotropic (i.e., liquid crystal in solution). Liquid crystal polymers are further characterized as having very stiff, rod-like molecules. In the quiescent state, the molecules align themselves in an ordered array in local regions forming domains. The individual domains, on the other hand, exhibit completely random orientations.
As a result of their ability to form anisotropic solutions, liquid crystal polymers can be spun into fibers in which the polymer molecules are highly oriented in the fiber length direction. This orientation begins in the liquid states and results in the unusual property of lower viscosity at higher concentrations.
A number of liquid crystal polymers have been described in the prior art. For example, U.S. Pat. No. 4,772,678 to Sybert et al. teaches a process of the preparation of novel liquid crystalline extended chain polymer-strong acid compositions capable of being drawn through long air gap distances and spun at exceptionally high spin draw ratios. Fibers, film and other articles formed from these liquid crystalline compositions exhibit exceptionally high physical and heat resistant properties. Disclosed is reaction of a monomer having the general structure ##STR2## with a strong phosphoric acid such as polyphosphoric acid (PPA) to produce the liquid crystal polymer. These monomers are only two of a vast number of disclosed monomers.
U.S. Pat. No. 4,703,103 to Wolfe, et al. is assigned to CommTech International Management Corporation as is the above U.S. Pat. No. 4,772,678 and relates to a similar process and composition wherein the molecular weight as characterized by intrinsic viscosity is controlled.
Specific examples of heterocyclic liquid crystal polymers and processes for preparing such polymers are disclosed in U.S. Pat. Nos. 4,439,578; 4,606,875; 4,847,350; 4,886,873; and 4,898,924. Polyparaphenylene-terephthamide which is available commercially under the trademark KEVLAR.RTM. and processes for preparing the same are disclosed in U.S. Pat. Nos. 3,006,899; 3,063,966; 3,094,511; 3,232,910; 3,414,645; 3,673,143; 3,748,299; 3,836,498; and 3,827,998, among others.
Liquid crystal polymers having a bisoxozal-containing biphenol structure in which the oxazole rings extend from separate phenyl nucleic and thereby enhance the "rod-like" nature of the polymer chain and contribute to the rigidity of the polymer is heretofore unknown.